Turbine blade, erosion shield forming method, and turbine blade manufacturing method

ABSTRACT

A rotor blade including: a blade main body having a tip as the upstream end in the rotation direction, and a blade surface in contact with the tip and which is the upstream surface in the flow direction of a work fluid; and an erosion shield formed as a cladding portion using laser welding on the tip and the blade surface. The boundary between the main body and the erosion shield is shaped to approach the surface opposite of the blade surface as the boundary moves from the end facing the blade surface towards the tip, and the boundary includes a first arc that includes the end facing the blade surface and a second arc arranged more towards the tip than the first arc; the first arc is convex towards the inside of the main body and the second arc is convex towards the outside of the main body.

FIELD

The present invention relates to a turbine blade including an erosionshield, an erosion shield forming method, and a turbine blademanufacturing method.

BACKGROUND

In a general turbine (for example, steam turbine), a rotor that is arotational shaft is rotatably supported at a casing, turbine blades areinstalled at an outer peripheral portion of this rotor, also turbinevanes are installed at an inner wall of the casing, and the multipleturbine blades and turbine vanes are alternately arranged on a steampassage. Furthermore, the turbine blades and the rotor are rotationallydriven in a process in which steam flows in the steam passage.

The turbine blade includes a blade root portion fixed to a rotor disk ofthe rotor, a platform integrally formed with the blade root portion, anda blade portion having a base end portion joined to the platform andextending to a tip end portion side. Additionally, a plurality ofturbine blades is fixed at their base ends to an outer peripheralportion of the rotor disk so as to be arranged in a row in acircumferential direction thereof.

For example, turbine blades of a steam turbine are rotated inside aroute where steam flows. At this point, the steam near a final stage ofa low-pressure steam turbine includes a large amount of small waterdroplets. Therefore, a front edge portion of a blade tip end is thinneddue to erosion caused by high-speed collision of the water droplets.

As a countermeasure against such erosion, there is a method of formingan erosion shield at the front edge portion of the tip end of theturbine blade as disclosed in Patent Literature 1 and Patent Literature2, for example. In Patent Literature 1, an erosion shield is formed byapplying cladding by plasma transfer arc welding.

Furthermore, Patent Literature 2 discloses a technology in which hardmaterial powder is molten by high-density energy irradiation (laser andelectron beam) to form a hard layer by cladding by welding, and anerosion preventing portion (erosion shield) is provided by locallyreplacing a part of a member with the hard layer.

CITATION LIST Patent Literatures

Patent Literature 1: Japanese Laid-open Patent Publication No. 10-280907

Patent Literature 2: Japanese Laid-open Patent Publication No.2012-86241

SUMMARY Technical Problem

In the case of forming an erosion shield by arc welding as disclosed inPatent Literature 1, there may be a case in which a defect is generatedor hardness is not sufficient. Furthermore, erosion shield performancecan be improved by forming an erosion shield by cladding processing bylaser welding as disclosed in Patent

Literature 2. However, in the processing disclosed in Patent Literature2, there may be a case in which an erosion shield falls off from a blademain body and is damaged.

The present invention is provided to solve the above-described problems,and directed to providing a turbine blade including an erosion shieldhaving high resistance to erosion, an erosion shield forming method, anda turbine blade manufacturing method.

SOLUTION TO PROBLEM

According to the present invention, there is provided a turbine bladeinstalled in a turbine, comprising: a blade main body having a tip endwhich is an end portion in an upstream side in a rotational directionand a blade surface which is in contact with the tip end and which is asurface in an upstream side in a flow direction of working fluid; and anerosion shield which is formed by cladding by laser welding on at leastpart of the tip end and the blade surface of the blade main body,wherein a boundary between the blade main body and the erosion shieldhas a shape that approaches a surface opposite of the blade surface asthe boundary moves from an end portion on the blade surface towards thetip end in a cross-section perpendicular to an extension direction, andthe boundary includes a first arc which includes the end portion on theblade surface and a second arc which is arranged more towards the tipend side than the first arc, the first arc is convex towards inside ofthe blade main body, and the second arc is convex towards outside of theblade main body.

Preferably, the first arc and the second arc are smoothly connected inthe boundary.

Preferably, the second arc has a curvature which is larger than acurvature of the first arc.

Preferably, at least one or more arcs is arranged more towards the tipend side than the second arc.

Preferably, a thickness of the erosion shield at the tip end is thickerthan a thickness of the erosion shield between the first arc and thesecond arc.

According to the present invention, there is provided an erosion shieldforming method for forming an erosion shield on at least part of a tipend and a blade surface of a blade main body, the erosion shield formingmethod comprising: removing at least part of a tip end and an endsurface of a base body which is formed as a turbine blade to form aboundary; forming a cladding portion at the boundary by laser welding;and performing finish processing to remove an excess thickness portionof the base body and part of the cladding portion, wherein the boundaryhas a shape that approaches a surface opposite of the blade surface asthe boundary moves from an end portion on the blade surface towards thetip end, and includes a first arc which includes the end portion on theblade surface and a second arc which is arranged more towards the tipend side than the first arc, the first arc is convex towards inside ofthe blade main body, and the second arc is convex towards outside of theblade main body.

Preferably, in the base body, the excess thickness portion on the bladesurface has a thickness of 0.5 mm or more.

Preferably, in the base body, a thickness of the excess thicknessportion on the surface opposite of the blade surface is equal to orthicker than a thickness of the excess thickness portion on the bladesurface.

Preferably, the first arc and the second arc are smoothly connected inthe boundary.

Preferably, the second arc has a curvature which is larger than acurvature of the first arc.

Preferably, at least one or more arcs is arranged more towards the tipend side than the second arc.

Preferably, a thickness of the erosion shield at the tip end is thickerthan a thickness of the erosion shield between the first arc and thesecond arc.

According to the present invention, there is provided a turbine blademanufacturing method, comprising: manufacturing a base body by moldingthe base body with an excess thickness portion on a turbine blade; andforming an erosion shield on the blade main body by the erosion shieldforming method described above.

ADVANTAGEOUS EFFECTS OF INVENTION

According to the present invention, it is possible to achieve theerosion shield that maintains hardness while suppressing generation of adefect by forming the boundary between the blade main body and theerosion shield in the above-described shape. Consequently, resistance toerosion can be improved.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic structural diagram illustrating a steam turbineincluding a turbine blade.

FIG. 2 is a perspective view illustrating an outline structure of anembodiment of the turbine blade.

FIG. 3 is a cross-sectional view taken along A-A in FIG. 2.

FIG. 4 is an explanatory diagram to describe a shape and a formingmethod of an erosion shield.

FIG. 5 is a flowchart illustrating an exemplary turbine blademanufacturing method.

FIG. 6 is a schematic diagram illustrating an exemplary erosion shieldforming method of the turbine blade manufacturing method.

FIG. 7A is a schematic diagram illustrating an outline structure of acladding-by-welding device.

FIG. 7B is an enlarged view illustrating the outline structure of thecladding-by-welding device.

FIG. 8 is a flowchart illustrating an exemplary processing operation ofcladding by welding.

DESCRIPTION OF EMBODIMENTS

A preferred embodiment of the present invention will be described indetail below with reference to the attached drawings. Note that thepresent invention is not limited by the embodiment. Furthermore, in thecase where there are plural embodiments, a configuration combining therespective embodiments is to be included.

FIG. 1 is a schematic structural diagram illustrating a steam turbineprovided with turbine blades according to the present embodiment. In thefollowing, an outline of a structure of a steam turbine 1 according tothe present embodiment will be described with reference to FIG. 1.

As illustrated in FIG. 1, in the steam turbine 1, a casing 11 has ahollow shape, and a rotor 12 as a rotational shaft is rotatablysupported by a plurality of bearings 13. Turbine blades 15 and turbinevanes 16 are arranged inside the casing 11. A plurality of turbineblades 15 is arranged in a row and fixed in a circumferential directionof an outer periphery of a disk-shaped rotor disk 14 formed on the rotor12. A plurality of multiple turbine vanes 16 is arranged in a row andfixed to an inner wall of the casing 11 in a circumferential directionthereof. These turbine blades 15 and turbine vanes 16 are alternatelyarranged in an axial direction of the rotor 12.

Furthermore, inside the casing 11, the above-described turbine blades 15and turbine vanes 16 are arranged and a steam passage 17 through whichsteam passes is formed. In the steam passage 17, a steam supply port 18is formed as an inlet port to be supplied with steam, and a steamdischarge port 19 is formed as an outlet port to discharge steam.

Next, an outline of operation of the steam turbine 1 will be describedwith reference to FIG. 1. Steam supplied to the steam passage 17 fromthe steam supply port 18 of the steam turbine 1 expands in a process ofpassing the turbine vanes 16 and becomes high-speed steam current. Thesteam current having passed the turbine vanes 16 is blown to the turbineblades 15, and rotates the multiple turbine blades 15 and the rotor 12attached with these turbine blades 15. For example, a generator and thelike are connected to the rotor 12, and the generator is driven togenerate power by rotation of the rotor 12. The steam having passed aportion provided with the turbine vanes 16 and the turbine blades 15 inthe steam passage 17 is discharged from the steam discharge port 19.

FIG. 2 is a schematic diagram illustrating the turbine blade accordingto the present embodiment. FIG. 3 is a cross-sectional view taken alongA-A in FIG. 2. A structure of the turbine blade 15 of the presentembodiment will be described with reference to FIGS. 2 and 3. Asillustrated in FIG. 2, the turbine blade 15 includes a blade rootportion 21, a platform 22, and a blade portion 23. The blade rootportion 21 is embedded in the rotor disk 14, and the turbine blade 15 isfixed to the rotor disk 14. The platform 22 is a curved plate-likeobject integrally formed with the blade root portion 21. The bladeportion 23 has a base end portion fixed to the platform 22 and has a tipend portion extending to the inner wall side of the casing 11. The bladeportion 23 may be twisted in a blade length direction. Furthermore, theturbine blade 15 may include a shroud fixed to the tip end portion ofthe blade portion 23. The shroud is a member configured to contact ashroud of an adjacent turbine blade 15 to fix the turbine blade 15 orconfigured to suppress vibration of the turbine blade 15.

Here, in the turbine blade 15, an erosion shield 25 is formed at a partof a surface of a blade main body 24 as illustrated in FIGS. 2 and 3.The erosion shield 25 is formed in a front edge portion of the turbineblade 15 corresponding to an upstream side of the steam current whichflows by rotation of the turbine blade 15, that is, at a tip end 26 anda part of a blade surface 27 in the tip end 26 side. A borderlinebetween the blade main body 24 and the erosion shield 25 is to be aboundary 28. The erosion shield 25 may be provided in a certain range ona side which is distant from the platform 22 in an extension directionof the turbine blade 15, that is, in a direction of the blade portion 23separating away from the platform 22. In other words, the erosion shieldmay be formed only in a part located on a radially outer side duringrotation. For the erosion shield 25, for example, wear resistantcobalt-based alloy such as Stellite (registered trademark) mainlycontaining cobalt can be used. The erosion shield 25 can be formed byperforming cladding processing by laser welding (cladding by welding) onthe surface of the blade main body 24 with target material (for example,Stellite (registered trademark)). Furthermore, the blade main body 24 isformed of chromium-based alloy and the like.

Next, a more detailed shape of the erosion shield, an erosion shieldforming method, and a turbine blade manufacturing method will bedescribed with reference to FIGS. 4 to 8. FIG. 4 is an explanatorydiagram to describe the shape and the forming method of the erosionshield. FIG. 5 is a flowchart illustrating an exemplary turbine blademanufacturing method. FIG. 6 is a schematic diagram illustrating anexemplary erosion shield forming method of the turbine blademanufacturing method. FIG. 7A is a schematic diagram illustrating anoutline structure of a cladding-by-welding device. FIG. 7B is anenlarged view illustrating the outline structure of thecladding-by-welding device. FIG. 8 is a flowchart illustrating anexemplary processing operation of cladding by welding.

As illustrated in FIG. 4, in the turbine blade 15, a groove for formingthe erosion shield 25 is formed in a base body 40 for the blade mainbody 24 to form a boundary surface 28. After that, a material for theerosion shield 25 is formed by the cladding processing on the boundary28, and then an excess thickness at a portion formed by the claddingprocessing and an excess thickness of the base body 40 are removed,thereby forming the tip end 26, blade surface 27, and a surface oppositeof the blade surface 27.

Here, the boundary 28 is formed in a shape that comes closer to thesurface opposite of the blade surface 27 as its position approaches froman end portion on the blade surface 27 to an end portion of the tip end26. Furthermore, the boundary 28 is formed of: a curved surface (firstcurved surface) R1 located in the end portion on the blade surface 27side which is convex towards the inside of the blade main body 24; acurved surface (second curved surface) R2 which is located closer to thetip end 26 side than the first curved surface R1 and is convex towardsthe outside of the blade main body 24; a curved surface (third curvedsurface) R3 which is located closer to the tip end 26 side than thesecond curved surface R2 and is convex towards the outside of the blademain body 24; and a straight line which is located between the thirdcurved surface R3 and the surface opposite of the blade surface 27. Theboundary 28 of the present embodiment has the first curved surface R1,second curved surface R2, and third curved surface R3 smoothlyconnected. Furthermore, in the boundary 28 of the present embodiment, acurvature radius of the first curved surface R1 is smaller than acurvature radius of the second curved surface R2. Additionally, in theboundary 28, a curvature radius of the third curved surface R3 issmaller than the curvature radius of the first curved surface R1.

As an example of each shape of the turbine blade 15 of the presentembodiment, the curvature radius of the first curved surface R1 is 6.5mm, the curvature radius of the second curved surface R2 is 10.0 mm, andthe curvature radius of the third curved surface R3 is 2.5 mm.

In the boundary 28, a distance dl from a contact point between thesecond curved surface R2 and the third curved surface R3 to the surfaceopposite of the blade surface 27 is 2.3 mm, and a distance d2 of thestraight line located between the third curved surface R3 and thesurface opposite of the blade surface 27 is 0.7 mm. In the turbine blade15, a distance d3 from the blade surface 27 to a contact point betweenthe first curved surface R1 and the second curved surface R2 is 0.8 mm.In the base body 40, distances d4 and d5 between a surface facing theblade surface 27 and the blade surface 27 are 1.0 mm. A distance d6between a surface of the base body 40 facing the surface opposite of theblade surface 27 and the surface opposite of the blade surface 27 of theturbine blade 15 is 2.0 mm.

Furthermore, in the base body 40, a distance L1 from an end portion onthe tip end 26 side to the end portion of the boundary 28 on the bladesurface 27 side is 12.5 mm, and a distance L2 from the end portion onthe tip end 26 side to the contact point between the first curvedsurface R1 and the second curved surface R2 is 9.0 mm. In the base body40, a distance L3 from an end portion on the tip end 26 side to an endportion of the erosion shield 25 on the tip end 26 side is 1.0 mm. Inthe base body 40, a distance L4 from the end portion on the tip end 26side to an end portion of the third curved surface R3 on the tip end 26side is 2.7 mm. In the base body 40, a distance L5 from the end portionon the tip end 26 side to the contact point between the second curvedsurface R2 and the third curved surface R3 is 3.2 mm.

In the turbine blade 15, the boundary 28 between the blade main body 24and the erosion shield 25 is formed in the shape that comes closer tothe surface opposite of the blade surface 27 as the position approachesfrom the end portion on the blade surface 27 side to the end portion ofthe tip end 26, and includes the first curved surface R1 and the secondcurved surface R2, thereby erosion shield performance of the erosionshield 25 can be improved. Moreover, the blade main body 24 can beprevented from generation of a defect on the erosion shield 25, andhardness of the erosion shield 25 can be enhanced (more hardened). Thatis, dilution of a deposited material (metal of the erosion shield 25)with a parent material component (component of the blade main body 24)can be suppressed by the above-described relation between the blade mainbody 24 and the erosion shield 25 formed by the cladding by laserwelding. Thereby, reduction of hardness of the erosion shield can beinhibited. Therefore, degradation of performance of the erosion shieldcan be suppressed. Furthermore, the metal of the erosion shield 25 isprevented from being cracked due to the dilution of the deposited metalwith the parent material component. Additionally, welding defects suchas incomplete fusion between the erosion shield 25 and the blade mainbody 24 as well as a blowhole can be suppressed from occurring.

Furthermore, in the present embodiment, while the first curved surfaceR1 and the second curved surface R2 are made to contact each other, thestraight line portion may also be provided between the first curvedsurface R1 and the second curved surface R2. Furthermore, in the presentembodiment, a curved surface may be provided between the third curvedsurface R3 and the surface opposite of the blade surface 27. Here,preferably, the boundary 28 is formed in a manner such that the firstcurved surface R1, second curved surface R2, and third curved surface R3are smoothly connected and curvature radii become large. When therespective curved surfaces of the boundary 28 are made to have the largecurvature radii, thickness variation of the erosion shield 25 can bemade to be gradual in a direction along the boundary 28, and performanceof the erosion shield 25 can be improved.

In the turbine blade 15, the distance d3 is shorter than a distanceobtained by subtracting the distance L3 from the distance L4. In otherwords, the thickness of the erosion shield 25 on the tip end 26 side isthicker than that on the blade surface 27 side. With this structure, thethickness on the tip end 26 side where erosion is more likely to occurand an amount of thinning is large can be formed thick while thethickness on the blade surface 27 side where an amount of thinning issmall can be formed thin.

The distances d4, d5 between the surface of the base body 40 facing theblade surface 27 and the blade surface 27, namely, a distance of anexcess thickness portion on the blade surface 27 are set to 0.5 mm ormore. When the distance of the excess thickness portion on the bladesurface 27 is set to 0.5 mm or more, the surface can be prevented frombeing cracked at the time of processing. In the base body 40,preferably, the distance of the excess thickness portion on the bladesurface 27 is set to 1 mm. Processing can be efficiently performed bysetting the distance of the excess thickness portion on the bladesurface 27 to 1 mm, especially to 1 mm or more.

Preferably, the distance d6 between the surface of the base body 40facing the surface opposite of the blade surface 27 and the surfaceopposite of the blade surface 27 of the turbine blade 15, morespecifically, a thickness of an excess thickness portion on the surfaceopposite of the blade surface 27 is equal to or thicker than thethickness of the excess thickness portion on the blade surface 27. Bythus setting the thickness of the excess thickness portion on thesurface opposite of the blade surface 27 to equal to or larger than thethickness of the excess thickness portion on the blade surface 27,processing can be efficiently performed. Furthermore, in the base body40, preferably, a distance of the excess thickness portion on thesurface opposite of the blade surface 27 is set to 2 mm. Furthermore,processing can be efficiently performed by setting the distance of theexcess thickness portion on the surface opposite of the blade surface 27side to 2 mm, especially to 2 mm or more.

Next, the turbine blade manufacturing method will be described usingFIGS. 5 and 6. In the turbine blade manufacturing method, a shape and aprocessing amount of the base body 40 of a turbine blade are determinedbased on a shape of a turbine blade (rotor blade) to be manufactured(Step S20). More specifically, the shape and distances betweenrespective positions of the base body 40 set as illustrated in FIG. 4described above are determined, and the processing amount and aprocessing procedure are determined based on the shape.

In the turbine blade manufacturing method, after processing conditionsare determined, the base body 40 of the turbine blade is manufacturedbased on the determined conditions (Step S22). In other words, the basebody 40 that is a workpiece 82 illustrated in FIG. 6 is manufactured inthe turbine blade manufacturing method. The base body 40 has a shapebefore the boundary 28 is formed in which an excess thickness portionand a portion located outer than the boundary 28 on the tip end remain.The base body 40 is formed by casting. For example, forging stock (forexample, stainless and the like) heated up to a high temperature of arecrystallization temperature or higher is set inside a pair of upperand lower dies with the shape of the base body 40, and hot die forgingis performed. After the hot die forging is finished, a forged producthaving the shape of the base body 40 is molded. The manufactured basebody 40 of the molded and forged product in a high-temperature state iscooled, then unnecessary portions (burr) are removed, and then heatprocessing is applied to the forged product. Thereby, residual stressgenerated in the forged product in the preceding process (forgingprocess) and heat stress generated in the forged product in the coolingprocess can be released. In this manner, the base body 40 ismanufactured.

In the turbine blade manufacturing method, beveling for cladding bywelding is performed after manufacturing the base body 40 (Step S24). Inother words, beveling is performed for the workpiece 82 in FIG. 6, and apart 44 of a base body 42 is removed like a workpiece 84. Consequently,a portion on the tip end side of the base body 42 becomes as a curvedsurface formed along the boundary 28.

In the turbine blade manufacturing method, after beveling for claddingby welding, cladding processing is performed by laser welding (StepS26). In other words, the cladding by welding is applied to theworkpiece 84 in FIG. 6, and a cladding portion 46 is formed on the basebody 42 like a workpiece 86. The cladding portion 46 is formed of ametal (deposited metal) to be the erosion shield 25 in a range includingan area 50 in which the erosion shield 25 is formed. Furthermore, thecladding processing is performed by setting an extension direction ofthe turbine blade 15, namely, a direction vertical to the drawing sheetof FIG. 6, as one pass. Moreover, when the cladding processing in thenext pass is performed after the cladding processing in the previouspass, a processing position is moved in a direction indicated by anarrow 52. That is, the cladding processing starts from the end portionon the blade surface 27 in the area 50, and is gradually moved to thetip end 26, and ends up to the surface opposite of the blade surface 27.

In the turbine blade manufacturing method, a thickness of the area 50can be prevented from being thick by forming the surface formed with thecladding portion 46 of the base body 42 into the curved surface formedalong the boundary 28, and cladding portion in each position can beformed of the deposited metal for one pass (one layer). In other words,forming of the area 50 by multi-layer cladding by welding can beprevented, and also an area with reduced hardness in the area 50 cannotbe presented in the surface of the area 50. Here, in the turbine blademanufacturing method, cladding portion 46 in each position can be formedof one layer by setting the thickness of the area 50 to 2 mm or less.The area having reduced hardness is an area where the parent material ismixed with the deposited metal and also is an area where performance ofthe erosion shield 25 (anti-erosion performance) obtained by thedeposited metal is degraded.

Preferably, in the cladding portion 46, dilution with the parentmaterial (material of base body 42) is 10% or less. In the turbine blademanufacturing method, the dilution with the parent material (material ofbase body 42) can be made to 10% or less by forming the cladding portion46 by the cladding processing using laser described later. In theturbine blade manufacturing method, the deposited metal (the metal ofthe cladding portion 46, the metal to be the erosion shield 25) can beprevented from weld penetration by forming the surface formed with thecladding portion 46 of the base body 42 into the curved surface formedalong the boundary 28, and the dilution with the parent component(material of base body 42) can be surely made to 10% or less.Furthermore, the cladding portion 46 is formed such that adjacent weldbeads, namely, portions formed by adjacent passes overlap with eachother. Furthermore, when the weld bead contacts the base body 42,preferably, the weld bead is formed such that a portion contacting otherweld bead becomes larger than a portion contacting the base body 42. Thecladding processing by laser welding (cladding by welding) will bedescribed later.

In the turbine blade manufacturing method, finish processing to removean excess thickness portion is performed after performing the claddingprocessing (Step S28). That is, the finish processing is applied to theworkpiece 86 in FIG. 6, and an excess thickness portion 60 on the bladesurface 27 side, an excess thickness portion 62 on the surface oppositeof the blade surface 27, and an excess thickness portion 64 of thecladding portion 46 are cut off as shown by a workpiece 88.Consequently, the turbine blade 15 including the blade main body 24 andthe erosion shield 25 is formed. After that, required heat processing(e.g., solution heat treatment and aging treatment) and the like areapplied to the turbine blade 15, and required mechanical characteristicsare provided to the turbine blade 15.

Next, the cladding processing by laser welding in Step S26 will bedescribed more in detail using FIGS. 7A, 7B and FIG. 8. First, anoutline structure of a cladding-by-welding device 100 to perform thecladding processing by laser welding will be described using FIGS. 7Aand 7B. As illustrated in FIG. 7A, the cladding-by-welding device 100includes a laser irradiation device 102 and a powder supply device 104.Furthermore, the cladding-by-welding device 100 includes a positionadjustment mechanism, a mechanism to move a relative position withrespect to the base body 42, a mechanism to perform copy processing of aworking position, and the like in addition to the above-describedcomponents.

The laser irradiation device 102 includes a light source 112, an opticalfiber 114, and a laser processing head 116. The light source 112 is alight emitting source to output laser. The optical fiber 114 guides thelaser output from the light source 112 to the laser processing head 116.The laser processing head 116 outputs the laser guided by the opticalfiber 114. The laser processing head 116 faces the working position ofthe base body 42 as illustrated in FIG. 7B, and irradiates laser 202 tothe working position.

The powder supply device 104 includes a powder supply source 120, apowder supply line 122, an air supply source 124, an air supply line126, and a powder supply head 128. The powder supply source 120 is asupply source to supply the deposited metal. The powder supply source120 conveys the deposited metal as a mixed flow with air or the like,thereby performing supply to the powder supply line 122. The powdersupply line 122 supplies the mixed flow of the air and the depositedmetal supplied from the powder supply source 120 to the powder supplyhead 128. The air supply source 124 supplies inert gas as shielding gas(e.g., nitrogen and argon) at the working position, in the presentembodiment, nitrogen gas of 99.999%. The air supply line 126 suppliesthe shielding gas supplied from the air supply source 124 to the powdersupply head 128. The powder supply head 128 is a double tube nozzle inwhich a tube on an inner peripheral side and a tube on an outerperipheral side arranged on an outer periphery of the inner peripheralside are concentrically arranged. The powder supply head 128 injects,from the tube on the inner peripheral side, the mixed flow (powder) 204of the air and deposited metal supplied via the powder supply line 122,and injects, from the tube on the outer peripheral side, shielding air206 supplied from the air supply line 126. The powder supply head 128faces the working position of the base body 42 as illustrated in FIG.7B, and injects the powder 204 and the shielding air 206 to the workingposition.

The cladding-by-welding device 100 can weld the deposited metal includedin the powder 204 to the base body 42 by irradiating the laser 202 tothe working position of the base body 42 while supplying the powder 204.Furthermore, the cladding-by-welding device 100 can make an atmosphereat the working position to a predetermined atmosphere by injecting theshielding air 206 to the working position. More specifically,concentration of oxygen at the working position can be controlled.

Next, an exemplary processing operation of the cladding processing bylaser welding will be described using FIG. 8. Furthermore, theprocessing illustrated in FIG. 8 can be executed by automatic controlusing a program and the like.

In the turbine blade manufacturing method, the surface of the area forgrooving is treated by performing grinder processing (Step S40). Thedeposited metal to be welded by cladding by welding can be brought intoa state easily welded to the surface (boundary) of the base body 42 byperforming the grinder processing. In the turbine blade manufacturingmethod, thickness measurement is performed after the grinder processing(Step S42). In other words, a shape of an area to be formed with theerosion shield 25 is measured in the turbine blade manufacturing method.

In the turbine blade manufacturing method, copy processing of theworking position is performed after performing the thickness measurement(Step S44). The position to be provided with a weld bead by injectingthe deposited metal is specified irradiating the position with thelaser. This adjusts a route in which each head is relatively moved tothe base body 42.

In the turbine blade manufacturing method, preheating and interpasstemperature adjustment are performed after performing the copyprocessing (Step S46). In the present embodiment, heating or cooling asneeded is mainly performed such that the base body 42 reaches apredetermined temperature included in a range from 50° C. to 100° C. Inthe turbine blade manufacturing method, cladding by welding is performedafter performing preheating and temperature adjustment (Step S48). Morespecifically, cladding by welding by one-pass is performed by using thecladding-by-welding device 100.

In the turbine blade manufacturing method, interpass and interlayertreatment is performed after performing the cladding by welding (StepS50). More specifically, flux, dirt, and the like adhering to thesurface of the cladding portion 46 are removed. In the turbine blademanufacturing method, whether to finish the cladding by welding isdetermined after the treatment (Step S52). In other words, whethercladding by welding of all preset passes has been performed and thecladding portion 46 has been formed is determined. In the turbine blademanufacturing method, in the case of determining that the cladding bywelding is not finished (No in Step S52), the process returns to StepS44 to perform the processing from the copy processing and perform thecladding by welding for the next-pass.

In the turbine blade manufacturing method, in the case of determiningthat the cladding by welding is finished (Yes in Step S52), surfacetreatment for the weld bead is performed (Step S54). More specifically,flux, dirt, and the like adhering to the surface of the cladding portion46 are removed. After that, in the turbine blade manufacturing method,thickness measurement is performed (Step S56) to measure the shape ofthe cladding portion 46, and the processing ends.

In the turbine blade manufacturing method, highly-accurate processingcan be performed by performing the cladding processing by laser welding(cladding by welding) in the manner of the above-described processing,and occurrence of a defect and the like can be suppressed as well. Inthe turbine blade manufacturing method, processing accuracy can beimproved and a defect can be suppressed by performing Steps S40, S46,S50, and S54, but these steps may be omitted.

Furthermore, in the present embodiment, the copy processing is performedfor each pass, but the copy processing may also be performed only beforethe first cladding by welding. In this case, a shape of a weld beadformed in each pass is calculated by calculation, and a copying positionis determined based on this shape. Furthermore, in this case,preferably, a working position is obtained by a measurement instrumentand feedback control is performed based on a result thereof. This canprevent occurrence of position displacement of the working position. Themeasurement position may be located on an upstream side of the workingposition.

Furthermore, in the cladding-by-welding device 100, preferably, anirradiation angle of the laser is set to about 90 degrees relative to aplane of the working position of the base body or a tangent lineconnecting a projecting portion and projecting portion. Since theirradiation angle of the laser angle is set to about 90 degrees relativeto the plane of the working position of the base body or the tangentline connecting the projecting portion and the projecting portion closeto the working position (for example, connecting a projecting portion ofthe weld bead and a projecting portion of the base body), weldingfailure can be prevented and mixture of the parent material into thedeposited metal can be prevented.

Furthermore, the cladding-by-welding device 100 may oscillate theworking position. For example, the laser may be made to weave at a highspeed in a width direction (direction orthogonal to a pass) while thepowder is supplied to the working position in a band-like shape. Here,the high speed is a speed at which energy density distribution of thelaser at the working position becomes not convex shaped but rectangularshaped, and a diluted portion mixed with the parent material can beformed shallow. Weaving in the present embodiment is weaving performedat a frequency range from several tens Hz to several hundreds Hz.Consequently, the energy density distribution can be made flat, and aportion molten by the laser can be shallow and wide.

Additionally, in the above-described embodiment, the deposited metal issupplied as the powder, but may also be supplied by means of thermalspray, cold spray, and the like.

Furthermore, the present embodiment has been described for the turbineblade in the steam turbine as an application target, but not limitedthereto. The present embodiment is applicable to a manufacturing methodof a rotor blade in another rotary machine such as a gas turbine.

Reference Signs List

-   1 STEAM TURBINE-   11 CASING-   12 ROTOR-   13 BEARING-   14 ROTOR DISK-   15 TURBINE BLADE-   16 TURBINE VANE-   17 STEAM PASSAGE-   18 STEAM SUPPLY PORT-   19 STEAM DISCHARGE PORT-   21 BLADE ROOT PORTION-   22 PLATFORM-   23 BLADE PORTION-   24 BLADE MAIN BODY-   25 EROSION SHIELD-   26 TIP END-   27 BLADE SURFACE-   28 BOUNDARY-   40, 42 BASE BODY-   46 CLADDING PORTION-   60, 62, 64 EXCESS THICKNESS PORTION-   82, 84, 86, 88 WORKPIECE-   100 CLADDING-BY-WELDING DEVICE-   102 LASER IRRADIATION DEVICE-   104 POWDER SUPPLY DEVICE

1. A turbine blade installed in a turbine, comprising: a blade main bodyhaving a tip end which is an end portion in an upstream side in arotational direction and a blade surface which is in contact with thetip end and which is a surface in an upstream side in a flow directionof working fluid; and an erosion shield which is formed by a claddingportion using laser welding on at least part of the tip end and theblade surface of the blade main body, wherein a boundary between theblade main body and the erosion shield has a shape that approaches asurface opposite of the blade surface as the boundary moves from an endportion on the blade surface towards the tip end in a cross-sectionperpendicular to an extension direction, and the boundary includes afirst arc which includes the end portion on the blade surface, a secondarc which is arranged more towards the tip end side than the first arc,and a third arc which is arranged more towards the tip end side than thesecond arc, the first arc is convex towards inside of the blade mainbody, the second arc is convex towards outside of the blade main body,and the third arc is convex towards the outside of the blade main body.2. The turbine blade according to claim 1, wherein the first arc and thesecond arc are smoothly connected in the boundary.
 3. The turbine bladeaccording to claim 1, wherein the second arc has a curvature radiuswhich is larger than a curvature radius of the first arc.
 4. (canceled)5. The turbine blade according to claim 1, wherein a thickness of theerosion shield at the tip end is thicker than a thickness of the erosionshield between the first arc and the second arc.
 6. An erosion shieldforming method for forming an erosion shield on at least part of a tipend and a blade surface of a blade main body, the erosion shield formingmethod comprising: removing at least part of a tip end and an endsurface of a base body which is formed as a turbine blade to form aboundary; forming a cladding portion at the boundary by laser welding;and performing finish processing to remove an excess thickness portionof the base body and part of the cladding portion, wherein the boundaryhas a shape that approaches a surface opposite of the blade surface asthe boundary moves from an end portion on the blade surface towards thetip end, and includes a first arc which includes the end portion on theblade surface, a second arc which is arranged more towards the tip endside than the first arc, and a third arc which is arranged more towardsthe tip end side than the second arc, the first arc is convex towardsinside of the blade main body, the second arc is convex towards outsideof the blade main body, and the third arc is convex towards the outsideof the blade main body.
 7. The erosion shield forming method accordingto claim 6, wherein, in the base body, the excess thickness portion onthe blade surface has a thickness of 0.5 mm or more.
 8. The erosionshield forming method according to claim 6, wherein, in the base body, athickness of the excess thickness portion on the surface opposite of theblade surface is equal to or thicker than a thickness of the excessthickness portion on the blade surface.
 9. The erosion shield formingmethod according to claim 6, wherein the first arc and the second arcare smoothly connected in the boundary.
 10. The erosion shield formingmethod according to claim 6, wherein the second arc has a curvatureradius which is larger than a curvature radius of the first arc. 11.(canceled)
 12. The erosion shield forming method according to claim 6,wherein a thickness of the erosion shield at the tip end is thicker thana thickness of the erosion shield between the first arc and the secondarc.
 13. A turbine blade manufacturing method, comprising: manufacturinga base body by molding the base body with an excess thickness portion ona turbine blade; and forming an erosion shield on the blade main body bythe erosion shield forming method for forming an erosion shield on atleast part of a tip end and a blade surface of a blade main body, theerosion shield forming method comprising: removing at least part of atip end and an end surface of a base body which is formed as a turbineblade to form a boundary; forming a cladding portion at the boundary bylaser welding; and performing finish processing to remove an excessthickness portion of the base body and part of the cladding portion,wherein the boundary has a shape that approaches a surface opposite ofthe blade surface as the boundary moves from an end portion on the bladesurface towards the tip end, and includes a first arc which includes theend portion on the blade surface, a second arc which is arranged moretowards the tip end side than the first arc, and a third arc which isarranged more towards the tip end side than the second arc, the firstarc is convex towards inside of the blade main body, the second arc isconvex towards outside of the blade main body, and the third arc isconvex towards the outside of the blade main body.